We have proposed a protocol for conditional suppression of losses in direct quantum state transmission over a lossy quantum channel. The method works by noiselessly attenuating the input state prior to transmission through a lossy channel followed by noiseless amplification of the output state. The procedure does not add any noise hence it keeps quantum coherence. We demonstrated this protocol experimentally in the subspace spanned by vacuum and single-photon states, and considered its general applicability [Phys. Rev. Lett. 109, 180503 (2012)].
Noiseless loss suppression in quantum optical communication